The invention relates generally to methods and apparatus for selecting and creating a desired electrical characteristic. More particularly, the invention relates to methods and devices for creating a user-definable electrical characteristic between two or more terminals.
As electrical and electronic systems become increasing prevalent, the need for new and improved electrical/electronic test equipment also increases. Various forms of well-known test equipment found in many electronics labs include oscilloscopes, meters, voltage and current sources, and the like. A particular type of variable resistor device known as a xe2x80x9cdecade boxxe2x80x9d has been particularly common for several years. A xe2x80x9cdecade boxxe2x80x9d such as that disclosed in U.S. Pat. No. 4,227,172, (incorporated herein by reference) typically includes a number of dials or rotary switches that allow a user to select a particular resistance that is applied between two terminals. As the user rotates the switches, resistors of varying magnitudes are mechanically switched on or off as appropriate to create a desired output resistance. Conventional decade boxes typically exhibit a number of marked disadvantages, though, in that their functionality is relatively limited to selecting certain values for electrical resistance. Further, decade boxes are frequently inaccurate (especially at very low resistances) and are typically relatively expensive. Moreover, the reliability and accuracy of conventional decade boxes may degrade over time and with increasing use.
Various forms of electronic-controlled resistances are known, but none provide the advantages of the invention described herein. It is therefore desirable to create an accurate, low cost and easy-to-use method and apparatus for establishing a desired electrical characteristic (such as a resistance, capacitance, voltage, current or impedance) between two terminals.
According to various embodiments of the invention, a device having a variable output electrical characteristic includes first and second output terminals and a number of switching circuits, each switching circuit having two states. One of the states produces a first electrical effect (e.g. an increased resistance) between said first and second output terminals, and the other state produces a second electrical effect (e.g. no change in resistance) between said first and second output terminals. A processor generates control signals that are applied to the switching circuits to place the switching circuits into a desired state such that said variable output characteristic between said first and second terminals is set to a desired value, which may be input from a user.